• The Journal of the Acoustical Society of Korea
• /
• v.38 no.3
• /
• pp.321-327
• /
• 2019

The purpose of this study is paper is to improve the flow performance and to reduce the aerodynamic noise of air discharge system consisting of a centrifugal fan, ducts and a housing for the clothes dryer. Using computational fluid dynamics and acoustic analogy based on FW-H (Ffowcs-Williams and Hawkings) Eq., air flow field and acoustic fields of the air discharge system are investigated. To optimize aerodynamic performance and aerodynamic noise, the response surface method is employed. The two factors central composite design using the inflow and outflow angles of fan blades is adopted. The devised optimum design shows the reduction of turbulent kinetic energy in the ducts and the housing of the system, and as a result, the improved flow rate and reduce noise is confirmed. Finally, the experment using the proto-type manufactured usign the optimum design shows the increase of flow rate by 4.2 %.

• The Journal of the Acoustical Society of Korea
• /
• v.38 no.3
• /
• pp.266-274
• /
• 2019

As can be seen in the statistics on domestic performance facilities, small or large scale of acoustic renovations seem to be unavoidable in many of those facilities due to its senility. However it is hard to find case studies which can be referred to for its acoustic renovation process. This study tried to provide a case study example of acoustic renovation for a high school auditorium which has many restrictions as a cultural heritage building. Requirements from the client and acoustic problems found through a field measurement of existing space motivated acoustic design solutions and alternatives which can improve the acoustics of the space. The whole process from the initial stage of diagnosing acoustic problems to the final stage of a post acoustic evaluation after the completion of construction was described. The result from the post acoustic evaluation suggested that reverberation characteristics of the space as well as definition and clarity have been greatly improved by applying acoustic design solutions and alternatives. However, loudness of sounds in the space didn't reach the aimed level, which is due to the limited capability of slat ceiling structure for providing strong early reflections.

• The Journal of the Acoustical Society of Korea
• /
• v.25 no.3
• /
• pp.129-136
• /
• 2006

For the environmental noise assessments. A weighted equivalent noise level (LeqA) is used to measure the time varying environmental noise. However, it is not appropriately reflect various environmental noise features and human emotions. The human perception of the noise is affected largely by the psychoacoustic characteristics of noise as well as the sound pressure level In this study, the effective factors of noise qualify are analyzed using the subjective assessment and statistical analysis of environmental noise, such as road traffic noise. construction site noise, noise in daily living. and other. The analysis methodology is composed to three steps as follows : firstly, the values of the sound qualify metrics of various noise sources were analyzed. And to classify the noise sources, we conducted a cluster analysis using sound quality metrics. Secondly, subjective jury testing was carried out using the methods of paired comparisons and semantic differential. Finally, the correlation between the subjective parameters and the noise quality metrics were analyzed. As a result. the human perception characteristics of the various environmental noise are described in some physical parameters of the noise qualify metrics.

• The Journal of the Acoustical Society of Korea
• /
• v.28 no.6
• /
• pp.491-498
• /
• 2009

This paper presents the design method of an impedance matching network using an isolation transformer and the Chebyshev filter function for the high efficiency and the flat power driving of an underwater acoustic piezoelectric transducer. The proposed impedance matching network is designed for minimizing the reactance component of transducer and having the flat power response in the wide frequency range. We design a low pass filter with ladder-type circuit using the Chebyshev function as standard prototype filter function. In addition, we design the impedance matching network which is suitable for the equivalent circuit of transducer and the turn ratio of transformer through the bandpass frequency transformation. The proposed method is applied to the simulated dummy load of the tonpilz-type transducer operating in the middle frequency range. The simulation results are compared with the measured characteristics and the validity of the proposed method is verified.

• The Journal of the Acoustical Society of Korea
• /
• v.28 no.7
• /
• pp.646-652
• /
• 2009

In this paper, welding pitch optimization technique of vehicle subframe is presented considering the fatigue life of spot welding nuggets. Fatigue life of spot welding nuggets is estimated by using the frequency-domain fatigue analysis technique. The input data, which are used in the fatigue analysis, are obtained by performing the dynamic analysis of vehicle model passing through the Belgian road profile and also the modal frequency response analysis of finite element model of vehicle subframe. According to the fatigue life result obtained from the frequency-domain fatigue analysis, the design points to optimize the weld pitch distance are determined. For obtaining the welding pitch combination to maximize the fatigue life of the spot welding nuggets, 4-factor, 3-level orthogonal array experimental design is used. This study shows that the optimized subframe improves the fatigue life of welding nugget with minimum fatigue life about 65.8 % as compared with the baseline design.

• The Journal of the Acoustical Society of Korea
• /
• v.24 no.8
• /
• pp.469-480
• /
• 2005

There have been always some difficulties in target setting and conditioning of acoustic performances or the Korean traditional music hall due mainly to the lack of the information on the sound radiation characteristics of Korean musical sources. As the 2nd experiment succeeding the previous study[1], the radiation characteristics of eight typical Korean traditional musical sources were investigated if precision. The selected musical sources were Geomungo, Haegeum (string), Piri, Taepyeongso (woodwind), Buk, Kwaengguari, Jing (drum), and male Pansori Chang (vocal Performance). The results show that the directivity pattern of each instrument is different and has their own directivity characteristics. Measured directional and spectral characteristics of traditional Korean music sources were implemented into the computation of architectural acoustic measures. Significant differences in the acoustic measures at receiver positions were observed between the results in using the omni-directional source and the directional one. In order to investigate the acoustical characteristics of the instruments depending on the spatial variation four different shapes of halls were introduced including rectangular, fan. horse-shoe and geometrical shapes. Room acoustical parameters such as RT, SPL, C80, LF, STI were calculated at each type or hall. As the results, It was found that the rectangular hall has the most high clarity. lateral energy and STI values among low shapes of halls. It is thought that the suggested source data and design method can be used as a basic reference in the future acoustic design of performance halls for the Korean traditional music.

• The Journal of the Acoustical Society of Korea
• /
• v.35 no.2
• /
• pp.92-101
• /
• 2016

There are many results in which acoustical conditions of a classroom play an important role for studying effects and academic achievement of students. However, there are very few guidelines or design proposals which could make appropriate acoustic environment when classrooms are built or renovated. The present study suggests various design proposals satisfying acoustic standards of classrooms based on theoretical calculation and acoustic field experiments. At first, minimum area of sound absorption was calculated which is required to satisfy the acoustic standard for domestic middle and high schools. Also, room acoustic measurements were carried out in order to investigate the acoustic performance of an existing classroom by changing interior finishing materials on ceiling and rear walls. As a result, it was revealed that reverberation time standard below 0.8 s can be acquired even if there is no sound absorption on ceiling which is a general practice executed in Korea. Specially, it was found that if partial area of ceiling would be treated as reflective with the ratio of sound absorption and reflection as 2:1, almost similar acoustic parameters of $C_{50}$, $D_{50}$, RASTI (Rapid Speech Transmission Index) and higher sound levels could be acquired in comparison with the case of entire sound absorption on ceiling.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.6
• /
• pp.615-625
• /
• 2021

Prior to proposing appropriate standard for subway station platform, this study conducted field measurements to examine characteristics of room acoustics on platform of two subway stations. As a result of analyzing the longitudinal length of the platform, Sound Pressure Level (SPL) decreased (maximum difference : 14 dB), Reverberation Time (RT) tended to increase (maximum difference of 0.8 s ~ 1.5 s), and C50 and D50 were decreased (maximum difference: 5.9 dB ~ 9.1 dB and 31.8 % ~ 37.6 %, respectively) as measurement positions moved away from the sound source. The Interaural Cross-correlation Coefficient (IACC) did not show clear tendency, but it was lower than 0.3 in entire points. It is judged that the subway platform has non-uniform sound field characteristics due to various combinations of direct and reflective sound even though it is finished with a strong reflective material.This indicates that the room acoustic characteristics of the near and far sound field are clearly expressed depending on the source-receiver distances in the subway platform having a long flat shape with a low height compared to the length.Therefore, detailed architectural and electric acoustic design based on the characteristics of each location of speaker and sound receiver in the platform is required for an acoustic design with clear sound information at all positions of the platform.

• Journal of KSNVE
• /
• v.9 no.6
• /
• pp.1106-1115
• /
• 1999

This paper sums up the study of the soundproof facilities (noise barriers) to be placed on the test track section within the Seoul-Pusan H.S.T. project. The objective of this study is to determine optimum design of soundproof including height, length, location, sound absorbing materials for test track(chonan-taejon). This paper shows the model to design the shape and materials of noise barrier for high speed trains(TGV, ICE, ect). The design of soundproof facilities is to be conducted by MITHRA for the prediction of noise impact of the TGV and for optimising noise barriers in order to reduce the noise generated by high speed trains. A number of computer simulations are carried out in order to determine the specification of noise barrier on test track.

• The Journal of the Acoustical Society of Korea
• /
• v.36 no.5
• /
• pp.353-360
• /
• 2017

The single sensor based acoustic reflection control system separates the incident and reflected signals from the single sensor output, and reduces the reflected signal by generating an out-of-phase signal from the incident signal component. In this paper, we propose an optimal filter design method for a single sensor based reflection control system. In the proposed method, it is shown that the optimum control filter design is possible by using the measured impulse responses of the reflection and control paths. The reflection control algorithm based on the proposed optimal filter achieves better performance than the conventional adaptive filter-based algorithm and effectively controls the reflection without the initial convergence time. We performed computer simulations using the signals obtained in a 1-dimensional acoustic duct environment, and from the simulation results, it was confirmed that the proposed optimal filter has robust performance even in noisy environment.